"Locked" or "boltless" joints for restraining a pair of adjoining pipe lengths are known in the art.
One such type of joint comprises a spigot on one end of a pipe or fitting inserted into a bell mouth of another adjoining pipe or fitting and held fixed by lead or the like. This type of joint is generally rigid and does not permit or provide for angular deflection of the pipe lengths as caused by ground shifts or loads imposed thereon.
A further type of joint utilizes an annular resilient gasket disposed about the spigot. The gasket is held in compression between the spigot and bell mouth surfaces. The spigot and bell mouth are held locked against lengthwise axial displacement by metal clips molded into the sealing gasket and coacting upon being bent with grooves in the spigot to restrain separation of the pipe sections.
Another type of locked joint is a ball and socket joint. The spigot is deformed into a convex cylindrical surface which seats with a complementary concave surface in the bell mouth. An annular locking collar is provided on the spigot for locking engagement with the bell mouth.
A still further locked pipe joint is shown in U.S. Pat. No. 3,698,744 wherein an annular locking collar is disposed about the spigot and coacts with a bell mouth restraining flange to prevent axial separation of the pipe sections. The locking collar is mounted on the spigot to permit limited axial misalignment of the spigot and bell mouth longitudinal axis.